$\dfrac{3}{5} - \dfrac{1}{4} = {?}$
Solution: $ = {\dfrac{3 \times 4}{5 \times 4}} - {\dfrac{1 \times 5}{4 \times 5}} $ $ = {\dfrac{12}{20}} - {\dfrac{5}{20}} $ $ = \dfrac{{12} - {5}}{20} $ $ = \dfrac{7}{20}$